A philosophical term meaning a system of philosophy or an attitude of mind, which, denying the power of unaided humanreason to reach certitude, affirms that the fundamental act of humanknowledge consists in an act of faith, and the supreme criterion of certitude is authority.

Fideism has divers degrees and takes divers forms, according to the field of truth to which it is extended, and the various elements which are affirmed as constituting the authority. For some fideists, humanreason cannot of itself reach certitude in regard to any truth whatever; for others, it cannot reach certitude in regard to the fundamental truths of metaphysics, morality, and religion, while some maintain that we can give a firm supernatural assent to revelation on motives of credibility that are merely probable. Authority, which according to fideism is the rule of certitude, has its ultimate foundation in divine revelation, reserved and transmitted in all ages through society and manifested by tradition, common sense or some other agent of a social character. Fideism was maintained by Huet, Bishop of Avranches, in his work "De imbecillitate mentis humanae" (Amsterdam, 1748); by de Bonald, who laid great stress on tradition in society as the means of the transmission of revelation and the criterion of certitude; by Lamennais, who assigns as a rule of certitude the general reason (la raison générale) or common consent of the race (Défense de l'essai sur l'indifférence, chs. viii, xi); by Bonnetty in "Annales de philosophie chrétienne"; by Bautain, Ventura, Ubaghs, and others at Louvain. These are sometimes called moderate fideists, for, though they maintained that humanreason is unable to know the fundamental truths of the moral and religious orders, they admitted that, after accepting the teaching of revelation concerning them, human intelligence can demonstrate the reasonableness of such a belief. (cf. Ubaghs, Logicae seu Philosophiae rationalis elementa, Louvain, 1860).

In addition to these systematic formulae of fideism, we find throughout the history of philosophy from the time of the sophists to the present day a fideistic attitude of mind, which became more or less conspicuous at different periods. Fideism owes its origin to distrust in humanreason, and the logical sequence of such an attitude is scepticism. It is to escape from this conclusion that some philosophers, accepting as a principle the impotency of reason, have emphasized the need of belief on the part of humannature, either asserting the primacy of belief over reason or else affirming a radical separation between reason and belief, that is, between science and philosophy on the one hand and religion on the other. Such is the position taken by Kant, when he distinguishes between pure reason, confined to subjectivity, and practical reason, which alone is able to put us by an act of faith in relation with objective reality. It is also a fideistic attitude which is the occasion of agnosticism, of positivism, of pragmatism and other modern forms of anti-intellectualism. As against these views, it must be noted that authority, even the authority of God, cannot be the supreme criterion of certitude, and an act of faith cannot be the primary form of humanknowledge. This authority, indeed, in order to be a motive of assent, must be previously acknowledged as being certainly valid; before we believe in a proposition as revealed by God, we must first know with certitude that God exists, that He reveals such and such a proposition, and that His teaching is worthy of assent, all of which questions can and must be ultimately decided only by an act of intellectual assent based on objective evidence. Thus, fideism not only denies intellectualknowledge, but logically ruins faith itself.

It is not surprising, therefore, that the Church has condemned such doctrines. In 1348, the Holy See proscribed certain fideistic propositions of Nicholas d'Autrecourt (cf. Denzinger, Enchiridion, 10th ed., nn. 553-570). In his two Encyclicals, one of September, 1832, and the other of July, 1834, Gregory XVI condemned the political and philosophicalideas of Lamenais. On 8 September, 1840, Bautain was required to subscribe to several propositions directly opposed to Fideism, the first and the fifth of which read as follows: "Human reason is able to prove with certitude the existence of God; faith, a heavenly gift, is posterior to revelation, and therefore cannot be properly used against the atheist to prove the existence of God"; and "The use of reason precedes faith and, with the help of revelation and grace, leads to it." The same proposition were subscribed to by Bonnetty on 11 June, 1855 (cf. Denzinger, nn. 1650-1652). In his Letter of 11 December, 1862, to the Archbishop of Munich, Pius IX, while condemning Frohschammer's naturalism, affirms the ability of humanreason to reach certitude concerning the fundamental truths of the moral and religious order (cf. Denzinger, 1666-1676). And, finally, the Vatican Council teaches as a dogma of Catholicfaith that "one trueGod and Lord can be known with certainty by the natural light of humanreason by means of the things that are made" (Const., De Fide Catholicâ", Sess. III, can. i, De Revelatione; cf. Granderath, "Constitutiones dogmaticae Conc. Vatic.", Freiburg, 1892, p. 32 cf. Denzinger, n. 1806).

As to the opinion of those who maintain that our supernatural assent is prepared for by motives of credibility merely probable, it is evident that it logically destroys the certitude of such an assent. This opinion was condemned by Innocent XI in the decree of 2 March, 1679 (cf. Denzinger, n. 1171), and by Pius X in the decree "Lamentabili sane" n. 25: "Assensus fidei ultimo innititur in congerie probabilitatum" (The assent of faith is ultimately based on a sum of probabilities). Revelation, indeed, is the supreme motive of faith in supernaturaltruths, yet, the existence of this motive and its validity has to be established by reason. No one will deny the importance of authority and tradition or common consent in human society for our knowledge of natural truths. It is quite evident that to despise the teaching of the sages, the scientific discoveries of the past, and the voice of common consent would be to condemn ourselves to a perpetual infancy in knowledge, to render impossible any progress in science, to ignore the social character of man, and to make humanlife intolerable: but, on the other hand, it is an error to make these elements the supreme criteria of truth, since they are only particular rules of certitude, the validity of which is grounded upon a more fundamental rule. It is indeed true that moral certitude differs from mathematical, but the difference lies not in the firmness or validity of the certainty afforded, but in the process employed and the dispositions required by the nature of the truths with which they respectively deal. The Catholic doctrine on this question is in accord with history and philosophy. Rejecting both rationalism and fideism, it teaches that humanreason is capable (physical ability) of knowing the moral and religious truths of the natural order; that it can prove with certainty the existence of God, the immortality of the soul, and can acknowledge most certainly the teaching of God; that, however, in the present conditions of life, it needs (of moral necessity) the help of revelation to acquire a sufficient knowledge of all the natural truthsnecessary to direct humanlife according to the precepts of natural religion (Conc. Vatic., "De Fide Cath.", cap. ii; cf. St. Thomas, "Cont. Gent.", Lib. I, c, iv).

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